The present invention relates to devices and methods for removing oil from the surface of a water body, and more particularly to devices and methods for removing oil from drum skimmers below the surface of water bodies.
When oil is spilled into a water body, such as through damage to an oil tanker, the spilled water tends to form a thin film on the surface of the water body. This film is sometimes referred to as an oil slick or sheen. Oil films are detrimental to the marine environment, and can further damage shorelines if allowed to drift ashore.
Many different apparatuses and methods have been developed for collecting spilled oil from the surface of water bodies. One apparatus that has found widespread use for collecting spilled oil is the drum skimmer. Prior art drum skimmers consist generally of a cylindrical drum that is rotatably mounted on a floating vessel or on a platform. The longitudinal axis of rotation of the drum is preferably mounted substantially parallel to the surface of the body of water. A lower portion of the drum is partially submerged in the body of water. As the drum rotates through oil floating on the surface of the water body, oil adheres to the surface of the drum. Oil is then removed from the surface of the drum, typically by use of a scraper or wiper blade, and is diverted into a collection tank or hopper for disposal. Examples of rotating drum oil and related collection devices can be found in U.S. Pat. No. 3,576,257 (Yates); U.S. Pat. No. 3,685,653 (Van Stavern et al.); U.S. Pat. No. 3,947,360 (Fast); U.S. Pat. No. 4,013,561 (Murphy); U.S. Pat. No. 4,173,536 (McCall); U.S. Pat. No. 4,514,299 (Ayroldi); U.S. Pat. No. 4,957,636 (Wilson); U.S. Pat. No. 5,030,363 (Pole); U.S. Pat. No. 5,522,990 (Davidian); U.S. Pat. No. 5,380,431 (Newsom); 5,618,420 (Stella).
Up to now, prior art drum skimmers have focused on scraping or wiping oil from the drum surface at points above the surface of the water. Through observation of drum skimmers, the inventor has discovered that as oil is pulled underwater along the surface of the drum, the oil remains adhered only on the downwardly turning half of the drum. Large amounts of oil are pulled under on the downwardly turning half of the drum. However, as soon as a point of the drum passes from the downwardly turning half to the upwardly turning half of the drum, oil rapidly begins to fall back into the water. At the point where the upwardly turning half of the drum exits the water, only a thin film of oil remains adhered to the surface of the drum. Prior art apparatuses and methods have been directed to scraping off or otherwise removing this thin film oil, at locations above the surface of the water body. It is believed that the problem of oil loss on the upwardly turning half of the drum was unknown to prior practitioners of the art. The present invention provides apparatuses and methods for solving the problems associated with oil loss, and in doing so takes advantage of certain heretofore unknown features of the oil loss phenomenon.
Through further experiments and observations, the inventor has also discovered that dry drums collect oil much more efficiently than wet drums. Accordingly, apparatuses and methods for drying the outer surface of drums are incorporated herein.
There is thus a need for an oil collection apparatus having the following characteristics and advantages over the prior art.
It is an object of the invention to provide an oil collection apparatus that collects oil from a surface of a water body by scraping a drum below a surface of the water body.
It is another object of the invention to provide an oil collection apparatus that improves oil collection by wiping water from the surface of unsubmerged regions of the drum.
Accordingly, an apparatus for collecting oil from a surface of a water body is provided comprising, generally, a drum, the drum rotatably mounted on a vessel such that a lower portion of the drum is positioned below a waterline of the vessel, and a wiper member on the vessel, the wiper member positioned and configured to wipe the drum below the waterline to thereby wipe oil from the drum below the surface of the water body. In order to collect the wiped oil, the vessel is provided with an oil collection tank. The oil collection tank has an open bottom. The open bottom is positioned below the water line of the vessel. The oil collection tank is positioned such that wiped oil flows through the open bottom and into the oil collection tank. The vessel is also provided with an oil deposit tank. The oil deposit tank has a closed bottom. The closed bottom is positioned below the waterline of the vessel. An oil transfer opening is provided between the oil collection tank and the oil deposit tank. The oil transfer opening is positioned to drain wiped oil from the oil collection tank into the oil deposit tank. In order to minimize draining of water from the collection to the deposit tank, a weir can be positioned in the oil deposit tank along the oil transfer opening. An oil storage tank is also provided. In one preferred embodiment, the oil storage tank is incorporated into the vessel. However, when the apparatus is used in the form of a pit skimmer, the oil storage tank can be separate from the apparatus (e.g. an oil tank, a tanker truck, or a barge). A pump or siphon is provided for transferring wiped oil from the oil deposit tank to the oil storage tank.
In order to improve uptake of oil during rotation of the drum, a dryer wiper member can be provided on the vessel. The dryer wiper is positioned to wipe water from an unsubmerged portion of the drum to thereby dry the drum.
In one preferred embodiment, the apparatus is provided with a second drum and a second wiper member, in the manner described above. The first drum and the second drum are preferably positioned on opposite sides of the oil collection tank.